The objectives of the proposed research are four-fold: a. To further define the relationship between structure and function in transfer RNA (tRNA) biochemistry; i.e., to correlate changes in nucleotide sequence or in nucleotide modification with functional changes of the molecule. b. To further define the genetics of tRNA, in terms of: 1. Location and number of copies of tRNA genes; 2. Clustering and distance between tRNA genes; 3. Regulatory genes, operators, promoters; 4. Location and regulation of tRNA modifying enzyme genes. c. To investigate the mechanism of transcription of tRNA genes, in terms of the nature of tRNA precursors, their size, nucleotide sequence, number of tRNA molecules per precursor molecule, cleavage, and modification. The nature of the initiation and termination sites for tRNA transcription will thus be studied. d. To investigate possible regulatory functions of tRNa, by studying the nature of pleiotropic effects induced in cells by mutations in tRNA genes, and the mechanism of secondary mutations which relieve that pleiotropy.